Removed conditional use of std::mutex instead of std::shared_mutex on MacOS.
Because MacOS < 10.12 did not support std::shared_mutex, a previous commit
naïvely substituted std::mutex, which does not have the same behavior.
Reverses PR #8273, which substitues std::mutex for std::shared_mutex on
macOS, and results in several bugs that seem to only affect MacOS
- https://bugs.dolphin-emu.org/issues/11919
- https://bugs.dolphin-emu.org/issues/11842
- https://bugs.dolphin-emu.org/issues/11845
This change eliminates conditional code for MacOS in the core configuration
layer code and enables the use of modern language features that are more
secure and thread-safe.
S David